Nah, you'll be fine I am only maybe 20lbs lighter right now... and I can't say that I'm all that worried about being "too big" for any of my bikes. I do need to lose some weight, and I *am* trying, but we all know it's hard (harder still that I'm 20lbs heavier than I was LAST YEAR when I started.. ugh!)

I've seen some pretty large guys out there on carbon frames.. I read somewhere once that most men's frames are built assuming the rider will be 300lbs.